The present invention relates to a polyimide film containing small amounts of tin salts for improving adhesive properties and thermal durability.
Polyimide films are well-known for their outstanding properties such as heat resistance, low temperature resistance, chemical resistance, electrical insulation and mechanical strength. Such polyimide films are widely used as electrical insulating films and as flexible printed circuit substrates. In such applications, the polyimide films are usually bonded to a copper foil with an acrylic or epoxy adhesive and, therefore, good adhesion is an important property requirement. Polyimide films having high thermal durability are also desired for use as insulators, gaskets or other parts which are exposed to high temperature environments.
U.S. Pat. No. 4,742,099, issued to Nagano et al. on May 3, 1988, discloses a polyimide film containing from 0.1 to 2% of a titanium-based organometallic compound for improving adhesion. The polyimide film of the invention does not contain an organometallic titanium compound.
Macromolecules, 17, pp. 1627-1632 (1984) discloses a polyimide film containing from 1.6 to 6.6% tin (II) chloride or dibutyltin (II) chloride for reducing electrical resistivity of the film.
Polymer, 29, pp. 559-565 (1988) discloses an electrically conductive polyimide film containing 6.3% of a metallic tin (II) salt.
In the present invention, only small amounts of tin salts are used to improve adhesion as contrasted to the prior art which uses large amounts to improve electrical conductivity.
It is an object of the present invention to provide a polyimide film having improved adhesive properties and high thermal durability. It is another object of the invention to provide a polyimide film having improved adhesive properties when bonded to metal foils, such as copper foil, using an epoxy, acrylic or other heat-resistant resin adhesive.